An American Airlines spokesman recently told ABC News that its 33 deaths, injuries and lost dogs need to be put in perspective. The airline flies more than 100,000 pets a year, and has flown about 600,000 since the DOT started keeping track of deaths. The 33 reported incidents represent 0.0055 percent of all dogs that fly American.

"While we never want to have an incident with any animal, that fraction means the likelihood of it happening is quite literally nil on a statistical basis," spokesman Tim Smith said in an e-mail. "That does not mean we do not take seriously any problem that does occur. We do."

The deaths of these puppies are in addition to those 33 deaths.

American also asks owners of deceased animals for permission to perform autopsies.

"In the overwhelming majority of cases where that happened, the autopsy report clearly showed a pre-existing medical condition on the animal that the owner either did not know about, or chose not to tell us," Smith said. "We are confident that pet owners can, and do, count on us to provide good care and safe transportation for their pet."

Trips for Flying With Pets

Ed Perkins, a contributing editor at Smarter Travel and owner of two poodles, said flying is a really traumatic experience for an animal and advises against it.

"It's not a question of how to do it. Just don't do it," Perkins said. "Drive instead or leave the pet at a kennel or with a friend or a sitter."

Of the 122 deaths on U.S. airlines in the past four years, 25 were English bulldogs, 11 pugs, seven golden retrievers, seven Labradors and six French bulldogs, according to the DOT.

Dr. Marty Becker, a veterinarian who has co-authored more than 20 pet books, said those smaller-snouted dogs have "a lot difficulty breathing, and that's when they aren't under stress." If the pet is obese, that makes breathing even more troublesome.

Becker, the veterinarian, said that many pets have undetected medical problems that only surface after it's too late.

"Elderly pets might have a pre-existing condition that could only be discovered when put under the stress of flight," Becker said.

Some people still like sedate flying pets, but Becker said the sedatives often have complications and recommends against them.

"There's no one to check on them or offer help if something happens in the cargo hold," he said.

Flying With Your Dog

Flying with pets isn't as easy as just driving up to the airport with your dog and walking on the plane.

Airlines have lengthy lists of rules and regulations meant to ensure pet safety, but they can be somewhat daunting. The size of the pet, the number of other animals on the plane and the kind of aircraft are all limitations that can be imposed. And there are different rules for pets who fly in the cargo hold and those that are transported in the passenger cabin.

American Airlines, for instance, says animals brought inside the airplane must fit in carriers that are 19 inches long, by 13 inches wide and 9 inches high. Animals must be able to stand up, turn around and lie down in a natural position in the kennel.

Passengers can only bring one kennel with them, although two dogs or two cats of the same species can be in the same kennel as long they weigh no more than a combined 20 pounds.